liver as a storage organ

Question 1

how is excess glucose stored

Answer 1

in the liver as glycogen

Question 2

what stimulates glucose storage

Answer 2

insulin releaseq

Question 3

how much of glycogen is stored in the liver

Answer 3

around 100g

Question 4

how much of glycogen is stored in skeletal muscle

Answer 4

300g

Question 5

describe process of synthesis of glycogen

Answer 5

1. Glucose is converted to Glucose-6-P by glucokinase (hexokinase in skeletal muscle)
2. Glucose-6-P is converted to Glucose-1-P by phosphoglucomutase
3. Glucose-1-P is then converted to UDP-Glucose
4. Finally UDP-glucose is added to the glycogen chain within the liver either by glycogen synthase or branching enzym

Question 6

what are the lipid soluble vitamins

Answer 6

A, D, E , K

Question 7

where are lipid soluble vitamins stored

Answer 7

in the liver

Question 8

how is vitamin A stored

Answer 8

stored within stellate cells in the liver as retinyl ester

Question 9

what is the active form of vitamin A

Answer 9

retinol

Question 10

how is the active form of vitamin A converted to the storage form

Answer 10

by lecithin:retinol acyltransferase.

this provides an easily retrievable source of Vitamin A and regulates its availability for other pathways

Question 11

what is retinol recycling

Answer 11

vitamin A may be stored or removed from storage several times a day, regulating the amount in circulation and preventing damage that may occur as a result of excess

Question 12

functions of vitamin A (4)

Answer 12

1. Formation of the photoreceptor rhodopsin
2. Signalling molecule within gene transcription
3. Normal function of the immune system
4. Mobilisation of iron stores for red blood cell production

Question 13

sources of vitamin D

Answer 13

either produced in body - (cholecalciferol)

or

found in food - (ergocalciferol)

Question 14

what happens to vitamin D in the liver

Answer 14

it must be metabolised in the liver before becoming the active form

Question 15

functions of vitamin D (3)

Answer 15

1. Maintaining normal serum calcium and phosphate concentrations
2. Increased absorption of calcium in the kidneys and intestines
3. Increased mobilisation of calcium from bone , activating osteoclasts to release more calcium

Question 16

what is vitamin E

Answer 16

a family containing various chemicals, including anti-oxidants.

Question 17

where is vitamin E stored

Answer 17

in either the liver or adipose tissue

Question 18

functions of vitamin E (3)

Answer 18

1. Antioxidant
2. Preventing propagation of free radicals
3. Protects Vitamin A

Question 19

how many forms of vitamin K are there

Answer 19

there are two forms of Vitamin K depending on whether they are obtained from plant or meat sources.

Question 20

functions of vitamin K (2)

Answer 20

1. Important for synthesis of clotting factors II, VII, IX and X
2. Co-factor for enzymes

Question 21

where is vitamin B12 typically found

Answer 21

in animal products

Question 22

how much of vitamin B12 is stored in the body

Answer 22

2-5%

with around 50% of this being in the liver

Question 23

functions of vitamin B12 (3)

Answer 23

1. Production of DNA and RNA
2. Maintaining healthy neurones
3. Red blood cell production – alongside Vitamin B9

Question 24

which minerals are stored in the liver

Answer 24

iron and copper minerals

Question 25

why is excess iron stored in the liver

Answer 25

because iron levels within the body need to be tightly regulated

Question 26

where is most iron within cells stored

Answer 26

in ferritin - a protein produced by the liver. All cell types within the liver can store iron however the majority is stored within hepatocytes.

Question 27

what happens in severe iron overload

Answer 27

the ferritin storage becomes saturated and so excess becomes stored within haemosiderin. However haemosiderin is a large, insoluble complex and iron stored within it is difficult to mobilise effectively.

Question 28

why do water-soluble vitamins require more regular intake than fat-soluble vitamins

Answer 28

because they pass more readily through the body

Question 29

why is iron essential

Answer 29

used in haemoglobin, myoglobin & bone marrow

Question 30

sources of iron

Answer 30

meat, liver, shell fish, egg yolk, beans, nuts and cereals

Question 31

where is homeostatic control of iron balance

Answer 31

in the intestinal epithelium, in the DUODENUM - which actively absorbs IRON from ingested foods

Question 32

how much of ingested iron is absorbed into blood stream

Answer 32

about 10% each day

Question 33

how are iron ions transported to duodenum

Answer 33

via active transport into the duodenal intestinal epithelial cells

Question 34

what happens to iron ions in duodenum

Answer 34

some iron ions are incorporated into FERRITIN - acts as an intracellular store for iron Most of the iron bound to ferritin in the intestinal epithelial cells is released back into the intestinal lumen when the cells at the tips of the villi disintegrate, and the iron is then excreted in the faeces

Question 35

what does iron absorption depend on

Answer 35

the body's iron content

Question 36

what happens when the body has stored enough iron

Answer 36

the increased concentration of free iron in the plasma and intestinal epithelial cells leads to an increased transcription of the gene encoding for ferritin and thus an increased synthesis of ferritin protein. results in an increased binding of Fe in the intestinal epithelial cells and a reduction in the amount of iron released into the blood

Question 37

what happens when body has low iron levels

Answer 37

the production of intestinal ferritin decreases resulting in a decrease in the amount of iron bound to ferritin thus increasing the unbound iron released into the blood

Question 38

what happens to unbound iron released into the blood

Answer 38

it circulates around the body bound to the plasma protein TRANSFERRIN Transferrin transports iron in the blood plasma to the bone marrow to be incorporated into new erythrocytes Once iron has entered the blood, the body has very little means of excreting it meaning it accumulates in tissues, most of the iron is stored in the LIVER in liver ferritin within KUPFFER CELLS (reticulo-endothelial macrophages)

Question 39

how much of total iron is haemoglobin

Answer 39

50%

Question 40

how much of iron is in heme containing proteins (mainly cytochromes)

Answer 40

25%

Question 41

how much of iron is in liver ferritin

Answer 41

25%